Commercial Air Transport (CAT) requirements dictate that an aircraft that operates over any substantial water routes is required to have multiple radios to cover multiple frequency ranges. For example, CAT aircraft are required to be dispatched with at least two fully functioning very high frequency (VHF) range radios and at least one high frequency (HF) range radio dedicated for voice communications only. Moreover, to allow for data communications capability and also to avoid maintaining spare radios at every destination airport, CAT aircraft typically carry at least three VHF radios for line-of-sight and terminal area voice and data communications, and at least two HF radios for long-range over-the-horizon voice and data flight deck communications. The VHF and HF radios allocated for data communications can be used for voice communications when spare radios are not available. As the use of data communications to operate the aircraft more efficiently becomes more important, a means to be able to dispatch aircraft with both voice and data communications capability while keeping the number of installed radios and sparing stations to a minimum is highly desirable.
Currently, in order for the aircraft to be able to maintain its communications capability in the event of total loss of engine power, one VHF radio and one HF radio are powered from an emergency power supply. The radios powered from the aircraft's emergency power supply are typically designated as VHF1 and HF1. These designations allow a flight crew to identify which set of radios to use for voice communications between the aircraft and ground stations in the event of total loss of aircraft engine power. However, should the VHF1 (HF1) fail before a total loss of engine power supply event occurs, the aircraft will be left without a means to communicate with the ground or other aircraft.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for improvements in aircraft radio communications systems.